Answers:
avast ,avg,etc etc
If you want a free anti-virus I recommend spick and span of popularity, but please choose the right one for you (install lone one):
1. AVG Free
a. A simple interface (easier to use than Avast! and Avira)
b. Can detect around 82.82% of viruses
Cons: low virus detection
2. Avast!
a. Real-time protection
b. It have an alternative to delete a virus once found
c. Can detect in the order of 87.46% of virus.
Cons: Too copious icon and confusing user interface
3. Avira AntiVir
a. It can detect malware better than Avast and AVG
b. It's cute umbrella icon
c. Can detect something like 94.26% of viruses
Cons: A thoroughly sluggish update
avast is pretty dutiful ...